This disclosure generally relates to a fuel vapor processing apparatus that may be mounted to a vehicle.
A fuel vapor processing apparatus has been widely known that may be mounted to a vehicle, such as an automobile, for inhibiting fuel vapor from diffusion to the atmosphere. Japanese Laid-Open Patent Publication No. 2004-225550 discloses a fuel vapor processing apparatus having a plurality of segmented adsorption chambers each containing an adsorbent. In this fuel vapor processing apparatus, one of the adsorbent chambers having a relatively large volume and a relatively large cross sectional area may contain adsorbent granules having a relatively large diameter, while the adsorbent chamber(s) disposed on the side of a purge port with respect the adsorption chamber having the relatively large volume and the relatively large cross sectional area may contain adsorbent granules having a relatively small diameter and a relatively high adsorption ability.
With the construction of the above noted Japanese publication, in which adsorbent granules having a relatively large diameter are contained in the adsorption chamber having a relatively large volume and a relatively large cross sectional area, an increase in size of the fuel vapor processing apparatus is necessary for achieving a sufficient adsorption amount of fuel vapor. In general, release of fuel vapor to the atmosphere from a fuel vapor processing apparatus may occur if a vehicle is parked even a whole day. It may be considered that the external atmospheric air may serve as a heat source to cause fuel vapor to be released from the fuel vapor processing apparatus. The adsorption chamber containing the adsorbent granules having the relatively large diameter disclosed in the above noted Japanese publication may have a relatively large void ratio. Therefore, in the case of the fuel vapor processing apparatus disclosed in the publication, there is a possibility that fuel vapor desorbed from the adsorbent due to the heat of the external atmospheric air may flow through gaps between adjacent adsorption granules to leak to the outside via the atmospheric port.
In view of the challenges discussed above, there is a need for inhibiting an increase of a resistance against flow of gas through a fuel vapor processing apparatus and for inhibiting fuel vapor from being discharged from an atmospheric port of a fuel vapor processing apparatus without accompanying an increase in size of the fuel vapor processing apparatus.